1. Field of the Invention
This invention relates to an optical unit controller suitable for controlling the driving of an optical unit using a motor, particularly such as a stepping motor.
2. Description of the Related Art
FIG. 5 shows the arrangement of the major portions of a camera using a stepping motor as a focusing actuator.
In FIG. 5 are illustrated a CPU 1 for performing control and operational processing of a camera operation sequence, a motor drive circuit 2 for driving a stepping motor 3, a photointerrupter 4 for detecting the position of a focusing lens 5 through a slit plate 6, the slit plate 6 fixed to the focusing lens 5, a switch 7a which is turned on by a first half stroke of a shutter release button to start photographing preparation operations (photometry and distance-measuring operations), a release switch 7b which is turned on by a second half stroke of the shutter release button to start a photographing operation (exposure operation), and a distance measuring circuit 8 for measuring the distance to an object to be photographed. The distance measuring circuit 8 has light emitting and receiving devices (not shown) such as an infrared ray emitting diode and a position sensitive device.
In this arrangement, the focusing lens 5 is normally set in an initial position. In this state, when the shutter release button is moved through its first half stroke to turn on the switch 7a, the CPU 1 drives the distance measuring circuit 8 to obtain distance measurement information, calculates the amount of driving of the focusing lens 5 from the distance measurement result, and drives the stepping motor 3 by the calculated driving amount through the motor drive circuit 2 to move the focusing lens 5 to a desired position.
Thereafter, when the release switch 7b is turned on by the second half stroke of the release button, the CPU 1 performs an exposure operation by shutter control. After the completion of the exposure operation, the focusing lens 5 is returned to the initial position. That is, the CPU 1 drives the stepping motor 3 a certain number of steps in the opposite direction through the motor drive circuit 2 to set the focusing lens 5 in the initial position (initial position setting).
For this initial position setting, the stepping motor 3 is driven a certain number of steps and then stopped, after the detection of an edge of the slit plate 6 by the photointerrupter 4.
FIGS. 6(a) and 6(b) comprise a diagram showing an example of drive patterns in a case where the stepping motor 3 is a two-phase motor.
In FIG. 6(a), the relationship between the number of steps (time) and the speed is shown, which is represented by three patterns, i.e., an acceleration pattern 1, a constant speed pattern 2, and a deceleration pattern 3. In FIG. 6(b), the relationship between time and phases is shown.
In the time period corresponding to the acceleration pattern 1, phase change time intervals are gradually reduced to gradually accelerate the rotation of the stepping motor 3. This is because if the pattern 1 is a drive pattern of abruptly accelerating the rotation of the stepping motor 3, the stepping motor 3 cannot rotate rapidly enough to follow the pattern. In the time period corresponding to the constant speed pattern 2, the phases are changed at equal time intervals, since the stepping motor 3 is in such a state as to be able to rotate so as to follow a high-speed-rotation drive pattern. In the time period corresponding to the deceleration pattern 3, phase change time intervals are gradually increased to gradually decelerate the rotation of the stepping motor 3, since if the pattern 3 is a drive pattern of abruptly stopping the rotation of the stepping motor 3, the stepping motor 3 cannot follow such a pattern because of an inertial effect, as in the case of the acceleration pattern 1.
As is apparent from the above, the numbers of steps for the acceleration pattern 1 and the deceleration pattern 3 are substantially equal to each other, and these numbers of steps (length of each pattern) are previously determined by the performance of the stepping motor 3.
The operation of setting the focusing lens 5 in the initial position by driving the above-described stepping motor 3 will be described with reference to FIGS. 7 through 9.
FIG. 7 shows the relationship between the positions of the photointerrupter 4 and the slit plate 6 when the focusing lens 5 is in the initial position.
If the focusing lens 5 is in a position such as shown in FIG. 8(a) when the exposure operation is completed, and if the focusing lens 5 is returned from this position to the initial position indicated by the broken lines in FIG. 8(a) (i.e., the position shown in FIG. 7), the relationship between the number of steps and the speed is as shown in FIG. 8(a).
In this case, as shown in FIG. 8(b), an initial position detection time when a right end edge of the slit plate 6 passes the photointerruptor 4, that is, the state of the photointerrupter is changed from "bright" to "dark" is in the period of the constant speed pattern 2.
If, as in this case, the time when the initial position is detected by the photointerrupter 4 is in the period of the constant speed pattern 2, the initial position detection time and the stepping motor 3 are in an in-phase relationship with each other. That is, the initial position detection time and the phase of the stepping motor 3 in setting the focusing lens 5 in the initial position are in phase with each other, as long as no step-out occurs.
However, if the position of the focusing lens 5 at the time when the exposure operation is completed is in the vicinity of the initial position, for example, as shown in FIG. 9(a), and if the focusing lens 5 is returned from this position to the initial position indicated by the broken lines in FIG. 9(a), the initial position detection time when the state of the photointerrupter 4 is changed from "bright" to "dark" will be in the period of the acceleration pattern 1.
If as in this case the initial position detection time is in the period of the acceleration pattern 1, the initial position detection time and the phase of the stepping motor 3 in setting the focusing lens 5 in the initial position vary due to a lag of the rotational speed of the stepping motor 3 with respect to the phase of the input to the motor 3, a lag of transmission of the rotation of the motor 3, for example, caused by a backlash of gears, and other factors, resulting in failure to accurately set the focusing lens 5 in the initial position.